Fluorine-containing polymers (i.e., fluoropolymers or fluorinated polymers), are an important class of polymers that include, for example, fluoroelastomers and fluoroplastics. Among this broad polymer class are polymers of high thermal stability, polymers of extreme toughness, and polymers exhibiting usefulness along a broad spectrum of temperatures. Many of these polymers also are almost totally insoluble in a wide variety of organic solvents; see, for example, F. W. Billmeyer, Textbook of Polymer Science, 3rd ed., pp. 398-403, John Wiley & Sons, New York (1984).
Fluoroelastomers, particularly the copolymers of vinylidene fluoride with other ethylenically unsaturated halogenated monomers such as hexafluoropropylene find particular utility in high temperature applications, such as in seal gaskets and linings. See, for example, Brullo, R. A., "Fluoroelastomer Rubber for Automotive Applications," Automotive Elastomer & Design, June 1985, "Fluoroelastomers Seal Up Automotive Future," Materials Engineering, October 1988, and "Fluorinated Elastomers," Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd ed., Vol. 8, pp. 500-515, John Wiley & Sons, New York (1979).
Fluoroplastics, particularly polychlorotrifluoroethylene, polytetrafluoroethylene, copolymers of tetrafluoroethylene and hexafluoropropylene, and poly(vinylidene fluoride), have numerous electrical, mechanical, and chemical applications. Fluoroplastics are useful, for example, as wire coatings, electrical components, seals, and in solid and lined pipes and piezoelectric detectors. See, for example, "Organic Fluorine Compounds," Kirk-Othmer, Encyclopedia of Chemical Technology, Vol. 11, pp. 20, 21, 32, 33, 40, 41, 48, 50, 52, 62, 70, and 71, John Wiley & Sons, New York (1980).
Multi-layer constructions containing a fluorinated polymer enjoy wide industrial application; multi-layer fluoropolymer constructions find utility in, for example, fuel line hoses and related containers and in retroflective sheeting materials. Increased concerns with evaporative fuel standards give rise to a need for fuel system components that have increased barrier properties to minimize the permeation of fuel vapors through automotive components including fuel filler lines, fuel supply lines, fuel tanks, and other components of the engine's fuel system control system. Various types of constructions have been proposed to address these concerns. In general, the most successful of these are co-extruded multi-layer constructions.
Multi-layer compositions comprising a fluorinated polymer layer and a polyamide or polyolefin layer are known. U.S. Pat. No. 4,933,090 (Krevor), for example, discloses laminate tubular articles that can comprise layers of fluorocarbon elastomers, and PCT Publication WO 93/1493 (LaCourt) discloses a laminar film structure comprising a polyimide and a fluoropolymer. The use of fluorinated polymers in retroreflective sheeting also is known. U.S. Pat. Nos. 3,551,025 and 4,348,312, for example, describe products that include glass microspheres, and PCT WO 95/11466 and WO 95/11464 describe products containing retroreflective cube corner arrays.
A variety of methods can be used to increase the adhesion between a fluorinated polymer layer and a polyamide or polyolefin layer. An adhesive layer can, for example, be added between the two polymer layers. U.S. Pat. No. 5,047,287 discloses a diaphragm, suitable for use in automotive applications, that comprises a base fabric having bonded to at least one surface a fluoro rubber layer by an adhesive that includes an acrylonitrile-butadiene or acrylonitrile-isoprene rubber having an amino group.
Surface treatment of one or both of the layers sometimes is employed to aid bonding. Some, for example, have taught treating fluoropolymer layers with charged gaseous atmosphere and applying subsequently a layer of a second material, for example a thermoplastic polyamide. E.g., European Patent Applications 0185590 (Ueno et al.) and 0551094 (Krause et al.) and U.S. Pat. Nos. 4,933,060 (Prohaska et al.) and 5,170,011 (Martucci).
Blends of the fluoropolymer and the dissimilar layer themselves are in some cases employed as an intermediate layer to help bond the two layers together. European Patent Application 0523644 (Kawashima et al.) discloses a plastic laminate having a polyamide resin surface layer and a fluororesin surface layer. The reference recognizes the difficulties encountered when making laminates having a polyamide layer and a fluororesin layer because of the incompatibility of the two materials. The laminate of the reference is prepared by use of an intermediate layer composed of a blend of an aliphatic polyamide resin with a fluorine-containing graft copolymer.
The addition of a di- or polyamine as an auxiliary bonding agent to a "tie" layer that comprises the dissimilar, non-fluorinated polymer also has been suggested to increase the degree of chemical bonding between the fluoropolymer and the non-fluorinated layer. To achieve its purpose, however, only those fluoropolymers and non-fluorinated polymers having some measure of reactivity with the di- or polyamine will result in an acceptable level of adhesion; polyolefins, for example, must be functionalized (typically with an anhydride, acid or alcohol group) to adhere to the fluoropolymer. Moreover, non-fluorinated polymers that are reactive with a di- or polyamine can suffer a significant change in physical properties by the amine reaction when employed to construct such a tie layer; polyurethanes, for example, can suffer a significant degradation in melt viscosity in the presence of even a minimal amount of a di- or polyamine, leading to a viscosity differential between the tie-layer it comprises and the other layers that can make it prohibitively difficult to co-process the multiple layers; and functionalized polyolefins can suffer a substantial loss of desirable physical properties in the presence of a di- or polyamine. A third significant drawback to the use of such tie layers lies in the use of the di- or polyamine itself. Because of its toxicity and allergenicity, the di- or polyamine is a difficult material to handle directly in any process, and any method that decreases the necessity of direct contact with a di- or polyamine would present a substantial benefit to the art.